How to Choose AA and Multi Battery Volt Testers
Digital, Analog, Self-powered, Alkaline, 9V, Load Testers
Oct 10, 2009
Most households have a battery problem. Disposable batteries are used in smoke alarm detectors, clocks, remote controls, flashlights and toys. Common problems include:
- New and old batteries getting mixed up in the drawer.
- Not knowing whether to replace or keep a battery: throw away a good battery or risk the battery running out of juice at a bad time (especially in the case of smoke detectors).
- Not knowing whether a device failed because it is faulty or because the battery is bad. If the device uses more than one battery, sometimes only one battery is bad but which one?
A battery tester is the solution to all these problems. Prices range from a few dollars to over $50. Popular brands include Radio Shack and IOGEAR (Juicemeter).
Battery Load Testers Versus Voltmeters
Voltmeters (commonly in the form of a multimeter) measure a battery's voltage more accurately than a cheap consumer battery tester. However an almost fully-discharged battery can have a relatively high voltage. A more accurate test of a battery's condition is to measure its voltage "under load", that is while drawing some current.
A "real" battery tester is therefore a combination voltmeter and load tester. The "load" can be a simple electrical resistor. Cheap battery testers can therefore give usefully accurate results. More sophisticated battery testers use clever electronics but the increased accuracy isn't necessarily needed by the average consumer.
Types of Batteries: AA, Alkaline, 9V, Button Cell
A battery tester needs to fit the battery's voltage and physical size. When choosing a tester, it is important to check that it will test the appropriate types of batteries.
Alkaline AA batteries are the most common, with a nominal 1.5 volts. Rechargeable NiMH AA batteries are lower at 1.2 volts and lithium AA batteries are higher at 1.7 volts. Other popular battery types are AAA, C, D, 9V, coin or button cell (1.5 volt, 3 volt), CR123A lithium and large lantern batteries.
Analog Versus Digital Battery Testers
Simple battery testers assume that only 1.5 volt alkaline batteries will be tested. More sophisticated testers have settings for different voltages.
Analog dial or swinging needle meters are simple but flexible. They have a green section on the scale marked out as "good", red for "replace battery". The advantage of an analog tester is that the user can use a felt pen to mark out his own readings for different types of batteries (alkaline, NiMH, lithium). New (or newly charged) batteries can be used to calibrate the tester, as can known half-discharged and almost fully discharged batteries.
There are different types of digital testers:
- Simple "idiot light" testers have a single LED for pass/fail indication. They don't give enough information to be very useful.
- Most digital testers have 3 to 5 LEDs or LCD bars, to represent different voltages or battery capacities. This will be good enough for most situations.
- Some digital testers have 10 or 20 LCD bars, making them almost as sensitive as an analog meter.
Self-powered and Powered Battery Capacity Testers
Most battery testers are "self-powered", drawing the power to run themselves from the battery that is being tested. This is convenient as they are always ready for use.
More sophisticated testers are powered by their own battery. While theoretically more accurate (some claim to display the percentage of remaining battery capacity), the inconvenience of having to replace the batteries will be a deal-breaker for the average consumer.
Multi or Universal Battery Testers
Most testers can test more than one type of battery.
- Slot designs have different slots for different battery types and sizes. They are easy to use but larger (because of multiple slots) and usually more expensive. They can only test a fixed number of battery types.
- Slide or hinge testers have a movable arm that is used to clamp the battery. They are small and light but keeping the battery in place can be difficult.
- Wire probe testers are like multimeters, using a large needle to make contact with the battery. They are the most flexible, being able to fit any battery, but are also harder to hold properly.
The Best Home Battery Tester
Flimsy construction, inaccurate results and inconsistent readings are common complaints with battery testers. Battery testers should therefore be tested with a new battery (a "known good" battery), and an almost fully discharged battery (can barely power a flashlight, motorized toy or electric shaver) before purchase.
Most importantly, the battery tester should be described by the manufacturer as a "load tester". If not, chances are that it is just a voltmeter. Whether a battery tester is analog or digital isn't as important as whether or not it is a load tester.
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